Circuit arrangement and method for synchronised transmission of audio data streams in a bus system

ABSTRACT

A circuit system ( 100 ) and a method for synchronized transmission of audio data streams in a bus system, in particular based on the IEEE 1394 Standard, by which, among other features, the sample data frequency of the data source may be recovered in the data sink without a PLL circuit system, including the following:  
     at least one data source ( 10 ) which provides audio data packets (AD) to be transmitted, in particular asynchronously and/or isochronously, in addition to frequency data packets (FS) which are associated with the particular audio data packets (AD) to be transmitted, and which are to be transmitted, in particular asynchronously,  
     having at least one clock or timer unit ( 12 ) for updating, in particular periodically, at least one synchronization cycle or time cycle in the circuit system ( 100 ); and  
     having at least one generator unit ( 14 ), which is connected ( 124 ) to the clock or timer unit ( 12 ) and which receives at least one data frequency (Fs),  
     for reading the particular counter status of the clock or timer unit ( 12 ) according to the data frequency (Fs),  
     for adding a predetermined, in particular constant, value to the counter status read,  
     for entering the value into the frequency data packet (FS), and for sending the frequency data packet (FS) after a predetermined number of values in the frequency data packet (FS) has been reached; and  
     at least one data sink ( 40 ) which is connected to the data source ( 10 ) via at least one data channel ( 30, 32 ) and which receives the audio data packet (AD) to be transmitted, in addition to the particular associated frequency data packet (FS),  
     having at least one clock or timer unit ( 42 ) for updating, in particular periodically, the synchronization cycle or time cycle,  
     having at least one audio data buffer unit ( 44 ) for entering the counter status of the received audio data packets (AD),  
     having at least one data frequency buffer unit ( 46 ) for entering the counter status of the received frequency data packets (FS);  
     having at least one comparator unit ( 48 ), which is connected ( 428 ) to the clock or timer unit ( 42 ) and is also connected ( 468 ) to the data frequency buffer unit ( 46 ),  
     for comparing the counter status of the clock or timer unit ( 42 ) to the counter status of the data frequency buffer unit ( 46 ) and  
     for sending at least one data frequency pulse (fs); and  
     having at least one output unit ( 50 ), which is connected ( 445 ) to the audio data buffer unit ( 44 ) and is also connected ( 485 ) to the comparator unit ( 48 ), for outputting the audio data pulse (ad) read from the audio data buffer unit ( 44 ) together with the data frequency pulse (fs) which is transmitted from the comparator unit ( 48 ) and which is associated with the audio data pulse (ad).

FIELD OF THE INVENTION

[0001] The present invention relates to a circuit system and to a method for synchronized transmission of audio data streams in a bus system, in particular based on the IEEE 1394 Standard.

BACKGROUND INFORMATION

[0002] Synchronization between data sources and data sinks in data buses which are based on asynchronous data transmission is achieved conventionally by the “time stamp” method. In this regard, methods have been developed for the IEEE 1394 Standard which likewise are based on the time stamp principle; the approach selected thus far, however, is based on the fact that the data source communicates the data sample rate to the data sink via a control channel before the transmission of the audio data begins.

[0003] Data packets having multiple audio data samples are subsequently transmitted via an isochronous data channel,. each data packet being provided with a “time stamp” which represents the presentation time of the first audio data sample. The sample data frequency must be recovered using a phase locked loop (PLL) circuit and using information about the number of data samples per data packet.

DESCRIPTION OF THE PRESENT INVENTION: OBJECT, SOLUTION, ADVANTAGES

[0004] Based on the disadvantages and shortcomings described above, the object of the present invention is to provide a circuit system and a method of the aforementioned type whereby the sample data frequency of the data source may be recovered in the data sink without a PLL circuit system. In addition, a goal of the present invention is to enable the transmission of multiple audio channels via the bus system in parallel and using different data sample rates. Lastly, it is also a goal of the present invention to enable the integration of externally synchronizable data sources and/or non-externally synchronizable data sources into the circuit system and into the method.

[0005] This object is achieved by a circuit system having the features stated in Claim 1, and by a method having the features stated in Claim 13. Advantageous embodiments and useful refinements of the present invention are characterized in the particular subclaims.

[0006] According to the teaching of the present invention, a synchronization mechanism for transmitting audio data in a bus system is provided for the circuit system and for the method. In this regard, one skilled in the art is in particular aware that a PLL circuit is not required for regenerating the (sample) data frequency in the data source. In addition, most of the jitters present in the bus system advantageously have no effect on the synchronization mechanism.

[0007] The synchronization mechanism provided by the present invention cannot be used for transmitting audio data based on the IEEE 1394 Standard, but instead is used for transmitting other types of data and/or for other applications requiring a fixed coupling between the data source and the data sink. However, the IEEE 1394 Standard in particular may still be used to achieve a rapid and uncomplicated data exchange, in particular in the entertainment field, between up to 63 devices currently at a maximum of 400 Mbit/second (up to 3,200 Mbit/second are planned).

[0008] For this type of data exchange, a fundamental distinction is made between asynchronous data transfer and isochronous data transfer.

[0009] In asynchronous data transfer, packets are first transmitted which contain the address of the data source and of the data sink. When the data sink receives the packet, it sends back an acknowledgement packet to the data source, and the transmission of the actual data packet is able to begin.

[0010] For isochronous data transfer, an isochronous channel in a specific band width is required between the data source and the data sink. An unambiguous channel identification number (channel ID) is assigned to this channel; the data source then transmits only the channel identification number, followed by the data, and the data sink receives only the data having this channel identification number, a maximum of 64 isochronous channels being possible. The remainder of the bandwidth not occupied by the isochronous transfer is available for the transmission of asynchronous data packets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Additional embodiments, features, and advantages of the present invention are explained in greater detail below, with reference to the exemplary embodiment illustrated by FIGS. 1 and 2.

[0012]FIG. 1 shows one embodiment of a circuit system according to the present invention, in a schematic diagram; and

[0013]FIG. 2 shows one possibility for the asynchronous transmission of three frequency data packets using the circuit system according to FIG. 1, in a schematic diagram plotted against time.

[0014] Identical or similar embodiments, elements, or features are provided with the same reference numbers in FIGS. 1 and 2.

BEST MODE OF IMPLEMENTING THE PRESENT INVENTION

[0015] The embodiment of a circuit system 100 according to the present invention, illustrated in FIG. 1, includes a data source 10 as the transmitting unit and a data sink 40 as the receiving unit, as well as an additional data source 20 to be explained in greater detail below. Data source 10, additional data source 20, and data sink 40 each function as bus nodes in the bus system in which circuit system 100 is situated.

[0016] In each of data source 10, in additional data source 20, and in data sink 40 a clock or timer unit 12, 22, or 42 is provided which in the case of a bus system based on the IEEE 1394 Standard is a “1394 timer,” i.e., a register containing the uniform time base for the entire data bus. The clock or timer unit 12, 22, or 42 is periodically updated with a frequency of approximately 8 Kilohertz, i.e., is set back to the value of the timing register contained in clock or timer unit 12.

[0017] In this regard it is important that this value not be set back even when the bus system is reset; this value is not set back to zero unless the timing register overflows. In general, the timing register contained in clock or timer unit 12 forms the basis for the synchronization.

[0018] One of the basic functions for both circuit system 100 and the method is carried out in generator unit 14 of data source 10 or in generator unit 24 of additional data source 20. Sample frequency (data frequency) Fs or Fs+ is present at one of the inputs of generator unit 14 or 24, respectively. For each cycle of data frequency Fs or Fs+, generator unit 14 or 24 reads the counter status from the timing register of clock or timer unit 12 or 22, adds a constant value, which is the transmission delay, thereto, and enters the value into an asynchronous frequency data packet FS or FS+.

[0019] This is illustrated by FIG. 2, which shows three asynchronous frequency data packets FS, each shifted in time with respect to one another (t3=t2+dt+μ=t1+dt+μ+dt+μ) by time interval dt+μ; it should be additionally noted here that a field which contains information about the contents of the data packet and about the synchronization method used in that instance is to be added in the header of the particular data packet.

[0020] After five values have been entered into asynchronous frequency data packet FS or FS+ according to the embodiment in FIG. 2, this asynchronous frequency data packet is transmitted to data sink 40 via data channel 32 or 38, respectively, either “unicast,” “broadcast to the group,” or “broadcast to all.” Data sink 40 enters the received values of transmitted frequency data packet FS into a data frequency buffer unit 46.

[0021] In a comparator unit 48 which likewise is associated with data sink 40, the counter states of clock or timer unit 42 arriving via connection 428 are now compared to the first value in data frequency buffer unit 46 arriving via connection 468. When these values are identical, a data frequency pulse fs is output by comparator unit 48 via connecting line 485, which in principle is again the sample frequency or data frequency Fs generated in data source 10, or the sample frequency or data frequency Fs+generated in additional data source 20.

[0022] Simultaneously with the transmission of frequency data packets FS or FS+, audio data packets AD or AD+ containing the associated audio data are transmitted via an asynchronous or isochronous data channel 30 or 34, respectively. These audio samples are entered in data sink 40 into an audio data buffer unit 44. Output unit 50, which likewise is associated with data sink 40 and which is designed in the form of an I2S output unit, for example, reads at every pulse from comparator unit 48 the instantaneous value from audio data buffer unit 44 via connection 445, and sends both values in the form of the audio data pulse and data frequency pulse fs, for example in the I2S format.

[0023] By using a data flow controller 60, which likewise is associated with data sink 40, it is possible to avoid idling operation or an overflow of audio data buffer unit 44 and/or data frequency buffer unit 46 in data sink 40. Data flow controller 60 includes a feedback loop to data source 10 (see the dashed line in FIG. 1); alternatively or in addition, data flow controller 60 may be used internally, i.e., in data sink 40, to damp the level of the audio signal in a timely manner during idling operation, in particular in audio data buffer unit 44, thus avoiding an interfering clicking sound in the loudspeaker.

[0024] A management unit designated in circuit system 100 in the form of an “audio master” manages a list of all sample frequencies or data frequencies transmitted, i.e., used in the bus system (for the embodiment according to FIG. 1, sample frequencies or data frequencies Fs or Fs+, respectively). If an additional data source 20 is now connected to the bus system, it must first be determined whether or not this additional data source 20 is externally synchronizable.

[0025] If this additional data source 20 is externally synchronizable, it must be further determined whether, in the bus system, data packets having the corresponding sample frequency or data frequency Fs+ are already being transmitted to additional data source 20. These mechanisms operate between the management unit and data source 10 or additional data source 20.

[0026] As indicated above, basically three cases may be distinguished with respect to additional data source 20:

[0027] In a first case, additional data source 20 is externally synchronizable, and sample frequency or data frequency Fs+ is already being transmitted; all data sources 10 having an identical sample frequency or data frequency Fs=Fs+ in the bus system are thus synchronized to the same cycle. In this case, additional data source 20 transmits audio data packets AD+ via asynchronous or isochronous channel 34; data sink 40 receives asynchronous frequency data packets FS=FS+ via channel 38, and generates sample frequency or data frequency Fs=Fs+, using clock or timer unit 42 and local comparator unit 48.

[0028] In a second case, additional data source 20 is not externally synchronizable, and the sample frequency or data frequency is not yet being transmitted. In this case, additional data source 20 generates the frequency data packets having the sample frequency or data frequency, using associated generator unit 24; additional data source 20 also generates audio data packets containing audio samples.

[0029] Lastly, in a third case additional data source 20 is not externally synchronizable, and sample frequency or data frequency Fs+ are already being transmitted. In this case, the management unit must determine whether all other data sources having this sample frequency or data frequency are externally synchronizable. When this is established, the management unit transmits to additional data source 20 the assignment to generate data packets containing the sample frequency or data frequency, and the second case previously described sets in; on the other hand, if all other data sources having this sample frequency or data frequency are not externally synchronizable, an additional sample frequency or data frequency is provided, and the second case previously described likewise sets in. 

What is claimed is:
 1. A circuit system (100) for synchronized transmission of audio data streams in a bus system, in particular based on the IEEE 1394 Standard, comprising at least one data source (10) which provides audio data packets (AD) to be transmitted, in particular asynchronously and/or in particular isochronously, in addition to frequency data packets (FS) which are associated with the particular audio data packets (AD) to be transmitted, and which are also to be transmitted, in particular asynchronously and/or in particular isochronously, having at least one clock or timer unit (12) for updating, in particular periodically, at least one synchronization cycle or time cycle in the circuit system (100); and having at least one generator unit (14), which is connected (124) to the clock or timer unit (12) and which receives at least one data frequency (Fs), for reading the particular counter status of the clock or timer unit (12) according to the data frequency (Fs), for adding a predetermined, in particular constant, value to the counter status read, for entering the value into the frequency data packet (FS), and for sending the frequency data packet (FS) after a predetermined number of values in the frequency data packet (FS) has been reached; and at least one data sink (40) which is connected to the data source (10) via at least one data channel (30, 32) and which receives the audio data packet (AD) to be transmitted, in addition to the particular associated frequency data packet (FS), having at least one clock or timer unit (42) for updating, in particular periodically, the synchronization cycle or time cycle, having at least one audio data buffer unit (44) for entering the counter status of the received audio data packets (AD), having at least one data frequency buffer unit (46) for entering the counter status of the received frequency data packets (FS); having at least one comparator unit (48), which is connected (428) to the clock or timer unit (42) and is also connected (468) to the data frequency buffer unit (46), for comparing the counter status of the clock or timer unit (42) to the counter status of the data frequency buffer unit (46) and for sending at least one data frequency pulse (fs); and having at least one output unit (50), which is connected (445) to the audio data buffer unit (44) and is also connected (485) to the comparator unit (48), for outputting the audio data pulse (ad) read from the audio data buffer unit (44) together with the data frequency pulse (fs) which is transmitted from the comparator unit (48) and which is associated with the audio data pulse (ad).
 2. The circuit system (100) as recited in claim 1, wherein the circuit system (100) is designed for the simultaneous transmission of the audio data packets (AD) and the frequency data packets (FS).
 3. The circuit system (100) as recited in claim 1 or 2, wherein at least one data flow controller (60) is provided for controlling the data flow between the data source (10) and the data sink (40).
 4. The circuit system (100) as recited in claim 3, wherein the data flow controller (60) is associated with the data sink (40); and/or the data flow controller (60) is connected (466) to the audio data buffer unit (44) and/or the data frequency buffer unit (46); and/or it is possible to prevent idling operation or an overflow of the audio data buffer unit (44) and/or the data frequency buffer unit (46) by using the data flow controller (60).
 5. The circuit system (100) as recited in claim 3 or 4, wherein the data flow controller (60) provides feedback to the data source (10), in particular to the generator unit (14) of the data source (10).
 6. The circuit system (100) as recited in at least one of claims 1 through 5, wherein at least one additional data source (20) is provided which provides audio data packets (AD+) to be transmitted, in particular asynchronously and/or isochronously, in addition to frequency data packets (FS+) which are associated with the particular audio data packets (AD+) to be transmitted; and has at least one clock or timer unit (22) for updating, in particular periodically, the synchronization cycle or time cycle; and has at least one generator unit (24) which is connected (224) to the clock or timer unit (22) and which is to receive at least one data frequency (Fs+), for reading the particular counter status of the clock or timer unit (22) according to the data frequency (Fs+), for adding a predetermined, in particular constant, value to the counter status read, for entering the value into the frequency data packet (FS+), and for transmitting the frequency data packet (FS+) after a predetermined number of values in the frequency data packet (FS+) is reached.
 7. The circuit system (100) as recited in claim 6, wherein the additional data source (20) is connected to the data source (10) via at least one data channel (34, 36) and is also connected to the data sink (40) via at least one data channel (38).
 8. The circuit system (100) as recited in claim 6 or 7, wherein at least one additional data flow controller is provided for controlling the data flow between the additional data source (20) and the data source (10).
 9. The circuit system (100) as recited in claim 8, wherein the additional data flow controller provides feedback to the additional data source (20), in particular to the generator unit (24) for the additional data source (20).
 10. The circuit system (100) as recited in at least one of claims 1 through 9, wherein at least one management unit is provided for managing the data frequencies (Fs, Fs+).
 11. The circuit system (100) as recited in at least one of claims 1 through 10, wherein at least one external data source is connectable.
 12. The circuit system (100) as recited in claims 10 and 11, wherein through data exchange between the management unit and the external data source, it is possible to determine whether the external data source is externally synchronizable.
 13. A method for synchronized transmission of audio data streams in a bus system, in particular based on the IEEE 1394 Standard, comprising the following steps: (a.1) updating, in particular periodically, at least one synchronization cycle or time cycle by using at least one clock or timer unit (12) which is associated with at least one data source (10); (a.2) supplying at least one generator unit (14), which is connected (124) to the clock or timer unit (12) and which is associated with the data source (10), with at least one data frequency (Fs); (b.1) reading of the particular counter status of the clock or timer unit (12) according to the data frequency (Fs), using the generator unit (14); (b.2) adding a predetermined, in particular constant, value to the counter status read; (b.3) entering the value into a frequency data packet (FS); (b.4) sending the frequency data packet (FS) after a predetermined number of values in the frequency data packet (FS) has been reached; (c.1) in particular, asynchronous and/or isochronous transmission of audio data packets (AD) between the data source (10) and at least one data sink (40) which is connected to the data source (10) via at least one data channel (30, 32); (c.2) in particular, asynchronous transmission of the frequency data packets (FS) associated with the particular audio data packets (AD) to be transmitted; (d.1) receiving the audio data packets (AD) to be transmitted, in addition to the respectively associated frequency data packets (FS), using the data sink (40); (d.2) updating, in particular periodically, the synchronization cycle or time cycle by using at least one clock or timer unit (42) associated with the data sink (40); (d.3) entering the counter status of the received audio data packets (AD) in at least one audio data buffer unit (44) associated with the data sink (40); (d.4) entering the counter status of the received frequency data packets (FS) in at least one data frequency buffer unit (46) associated with the data sink (40); (e.1) comparing the counter status of the clock or timer unit (42) to the counter status of the data frequency buffer unit (46), using at least one comparator unit (48) which is connected (428) to the clock or timer unit (42) and is also connected (468) to the data frequency buffer unit (46), and which is associated with the data sink (40); (e.2) sending at least one data frequency pulse (fs) by the comparator unit (48); and (f) outputting the audio data pulse (ad) read from the audio data buffer unit (44) together with the data frequency pulse (fs) which is transmitted from the comparator unit (48) and which is associated with the audio data pulse (ad), using at least one output unit (50) which is connected (445) to the audio data buffer unit (44) and is also connected (485) to the comparator unit (48), and which is associated with the data sink (40).
 14. The method as recited in claim 13, wherein the audio data packets (AD) and the frequency data packets (FS) are transmitted simultaneously.
 15. The method as recited in claim 13 or 14, wherein the data flow between the data source (10) and the data sink (40) is controlled by at least one data flow controller (60) which is connected (466) to the audio data buffer unit (44) and/or to the data frequency buffer unit (46), and which is associated with the data sink (40).
 16. The method as recited in claim 15, wherein idling operation or an overflow of the audio data buffer unit (44) and/or of the data frequency buffer unit (46) is prevented by the data flow controller (60).
 17. The method as recited in claim 15 or 16, wherein the data flow controller (60) provides feedback to the data source (10), in particular to the generator unit (14) of the data source (10).
 18. The method as recited in at least one of claims 13 through 17, characterized by the following steps: updating, in particular periodically, the synchronization cycle or time cycle by using at least one clock or timer unit (22) which is connected to the data source (10) via at least one data channel (34, 36) and is also connected to the data sink (40) via at least one data channel (38), and which is associated with at least one additional data source (20); supplying at least one generator unit (24) which is connected (224) to the clock or timer unit (22) and which is associated with the additional data source (20), with at least one data frequency (Fs+); reading of the particular counter status of the clock or timer unit (22) according to the data frequency (Fs+), using the generator unit (24); adding a predetermined, in particular constant, value to the counter status read; entering the value into a frequency data packet (FS+); and sending the frequency data packet (FS+) after a predetermined number of values in the frequency data packet (FS+) has been reached.
 19. The method as recited in claim 18, wherein the data flow between the additional data source (20) and the data source (10) is controlled by at least one additional data flow controller.
 20. The method as recited in claim 19, wherein the additional data flow controller provides feedback to the additional data source (20), in particular to the generator unit (24) of the additional data source (20).
 21. The method as recited in at least one of claims 13 through 20, wherein the data frequencies (Fs, Fs+) are managed by at least one management unit.
 22. The method as recited in at least one of claims 13 through 21, wherein at least one external data source is connected.
 23. The method as recited in claims 21 and 22, wherein data exchange between the management unit and the external data source is used to determine whether the external data source is externally synchronized. 